Donald Trump has chosen retired Marine General James Mattis to be defense secretary. Trump made the announcement during a victory rally in Cincinnati Thursday night. Donald Trump referred to retired General Mattis by his nickname “Mad Dog,” which he reportedly received after leading U.S. troops during the 2004 battle of Fallujah in Iraq. Mattis enlisted in the Marines at 19. He fought in the Persian Gulf War, in Afghanistan and then in Iraq, where he served as a major general. In May 2004, Mattis ordered an attack on a small Iraqi village that ended up killing about 42 people attending a wedding ceremony. Mattis went on to lead United States Central Command from 2010 to 2013, but the Obama administration cut short his tour over concerns Mattis was too hawkish on Iran, reportedly calling for a series of covert actions there. Mattis has drawn criticism over his apparent celebration of killing, including saying in 2005 about the Taliban, “It’s a hell of a lot of fun to shoot them.” Mattis only retired from the military in 2013, meaning he will need Congress to waive rules requiring defense secretaries to be civilians for seven or more years after leaving the military. The rules are in place to ensure civilian control over the U.S. armed forces. Already, New York Senator Kirsten Gillibrand has said she’ll vote against the waiver for General Mattis, saying, “Civilian control of our military is a fundamental principle of American democracy, and I will not vote for an exception to this rule.”